1. Field of the Invention
The invention relates to a machine tool comprising a vertical post, a head carrier mounted on said post and carrying at least one driven tool head, and a head changer having at least one head gripper movable into a changing position suited for the receipt of the tool head provided detachably at the head carrier.
2. Description of the Prior Art
There are known machine tools such as taught in German laid-open Patent Application No. 33 28 230 which may be composed of different units in accordance with the mechanical assembly technique, the vertical post including a head carrier to which a tool head may be fixed interchangeably. The vertical post or head carrier contains driving means to couple thereto a tool head such as a headstock, or a drill head, if the tool head is applied to the head carrier. A separate tool head magazine contains a number of tool heads. A head changer is adapted to grip each of the tool heads in order to deliver it to the head carrier of the vertical post, the head changer being mounted as a separate unit intermediate the head magazine and the vertical post of the machine tool. The head magazine is located on the rear side of the vertical post and is averted from the working position of the workpiece under treatment. Therefore, it is necessary to turn the vertical post about its vertical axis in order to move the tool head from the working into the changing position. While different unit-by-unit stages from a simple single axis working machine to a three axis machine with an automatic head changer and an automatic tool changer are implemented in known machine tool systems, it is mandatory to provide as a basic module in such systems a vertical post being rotatable about its vertical axis.
Even in case of the simplest variant of a single-axis working machine, a vertical post rotatable about its vertical axis has to be taken into consideration even though no benefit is derived therefrom, because rotatability of the vertical post becomes relevant only in case of an automatic changing system for tool heads within a more highly developed design. Nevertheless, even in the less developed working machine assembly, a rotary system and a corresponding drive in the post are required, producing a resultant increase in cost.
There are also known machine tools comprising a head carrier for a number of polygonally arranged tool heads of which each, by turning the head carrier, may be swivelled into a working position. It is possible to interchange the head carrier in total and, moreover, to exchange the individual tool heads at the head carrier. Yet a post rotatable about its vertical axis is also needed as a basic component of such machine tools.
Finally, there is known in the prior art a particular tool changing system taught in German laid-open Patent Application No. 33 29 539 wherein the vertical post supporting the tool head may be moved back from its working position. A rotatable ring assembled in the lower region of the post carries a number of head grippers. By rotating the ring about its vertical axis, the tool head is moved into a depositing position, and, by rotating it further, another tool head may be mounted to the post. Thus, for changing tools, translatory movements of the post and rotary movements of the ring are necessary. Further, in order to couple the tool heads to or to decouple them from the post, lifting movements have to be performed.
The known machine tools provided with interchangeable tool heads are disadvantageous because, in order to change a tool head, the vertical post has to be turned or be moved translatorily into a basic position, thus enabling the tool head to move from the working into the changing position. This action requires that large masses should be accelerated or decelerated. Moreover, subsequent to the turning movement of the vertical post, the head changer is subjected to a cycle of movements taking much time; time which is lost in processing of the workpiece.